Human granulocytes activated with serum treated zymosan (0.2 mg/ml) contract isolated human airways. The magnitude of the contraction depends on the number of granulocytes and the proportion of eosinophils among the granulocytes. The contraction is blocked by a leukotriene C4/D4 (LTC4/D4) receptor antagonist and by inhibition of lipoxygenase. This suggests that eosinophils rather than neutrophils are implicated in this response, which seems to be caused by LTC4/D4.